The present invention relates to a safety device for diesel engines which responds to an abnormal change of the ratio between the useful torque delivered by the diesel engine and the fuel quantity per power stroke. The latter is defined by the position of the control rod of the injection pump of the diesel engine.
Such a device has been described, for example, in British Pat. No. 764,608. With this known device, the position of the control rod of the injection pump of the diesel engine is converted directly into an electrical signal. However, this does not provide a signal proportional to the fuel quantity per power stroke throughout the entire range of the useful torque so that the known device is not in a position to distinguish the abnormal changes in the ratio of useful torque to fuel quantity. These changes might endanger operation, clearly from the other changes in this ratio.
Among these other changes is, for example, the change in the above-mentioned ratio which occurs with sudden changes of the useful torque where the speed-regulating device of the diesel engine increases or reduces the fuel quantity disproportionally. A fuel quantity proportional to the new useful torque will attain a settled value only after the so called control stabilization period.
Contrasting thereto, an abnormal change caused by a condition impairing the operation develops when the friction torque of the diesel engine suddenly rises, for example, due to jamming or seizing of a piston in its cylinder. In that case, the fuel quantity supplied per power stroke is no longer proportional to the useful torque because a disproportionately large amount of fuel must be supplied so that the engine may overcome its vastly increased internal friction torque.
An abnormal change caused by a condition which might impair operation also develops if one cylinder of the diesel engine does not fire, for example, due to a defective injection nozzle, and thus does not produce a useful torque. In that case, the remaining cylinders must take on the work of the missing cylinder, increasing the fuel quantity per power stroke while the useful torque remains the same.
Accordingly, it is the object of the present invention to provide a safety device which responds only to the disproportionality between fuel quantity and useful torque which occurs under conditions which might impair operation, but does not react to other disproportions occurring in normal operation.
Another object of the present invention is to provide a safety device of the foregoing character which is substantially simple in construction and may be economically fabricated.
A further object of the present invention is to provide a safety arrangement, as described, which may be readily maintained in service and which has a substantially long operating life.